Background context:

The anterior approach at L5-S1 has many advantages, however, vascular complications are challenging for spinal surgeons who may not be familiar with the variability of vascular anatomy. There are three different anterior approaches (intra-bifurcation approach and extra-bifurcation: left-, and right-sided pre-psoas approaches) described in previous studies to respond to the variability of anterior vascular anatomy for reduction in vascular injury, while no guidance for the choice of approach preoperatively.

Purpose:

To analyze the anatomical feasibility of three anterior approaches to access the L5-S1 disk space according to a practical framework.

Study design:

Retrospective study.

Patient sample:

Lumbar magnetic resonance imaging (MRI) from patients who visited our outpatient clinic were reviewed, with 150 cases meeting the inclusion criteria.

Outcome measures:

The following radiographic parameters were measured on axial T2-weighted MRI at the lower endplate of L5 and the upper endplate of S1: width of the vascular corridor, position of the left and right common iliac vein (CIV), and presence of perivascular adipose tissue (PAT). Moreover, we designed a safe line to evaluate the feasibility of left-, and right-sided pre-psoas approaches. Cases of lumbosacral transitional vertebrae were identified.

Methods:

The feasibility of the intra-bifurcation approach was determined by the width of the vascular corridor, presence of PAT, and the position of the CIV. The feasibility of the pre-psoas approach was determined by the relative position of the CIV to the safe line, presence of PAT, and the intersection point of the CIV and vertebral body.

Results:

68%, 64.7%, and 75.3% cases allowed the intra-bifurcation, left-, and right-sided pre-psoas approach to L5-S1, respectively. The cases in this study had at least one of three anterior approaches to access L5-S1 disk space, and 74% of cases had more than one anatomical feasibility of anterior approach. The right-sided pre-psoas approach was feasible in the majority of cases because of the vertical course of the right CIV with a significantly higher proportion of presence of PAT. Patients with lumbosacral transitional vertebrae (24 cases) may prefer the pre-psoas approaches, and only six cases (25.0%) were determined to be feasible for the intra-bifurcation approach.

Conclusions:

Our study proposes a practical framework to determine whether the three different anterior approaches are feasible access at L5-S1. According to the framework, all cases had the anatomical feasibility of using an anterior approach to access L5-S1, and three-fourths of cases had a replaceable anterior approach when encountering intraoperative difficulties.